Fainting (Syncope)
Fainting (Syncope): A Complete Patient Guide
Fainting (syncope) is a sudden, short loss of consciousness caused by a temporary drop in blood flow to the brain, followed by a quick and complete recovery. It is very common: around one in three people faint at some point in their lives. Most faints are harmless and are due to the body’s reflexes, but a minority are caused by a heart rhythm problem or heart disease, and these can be dangerous. The aim of assessment is to tell the two apart.
The 2018 ESC syncope guideline classifies fainting into three main groups:
Reflex (neurally mediated) syncope, including the common faint (vasovagal), situational faints and carotid sinus syndrome
Syncope due to orthostatic hypotension, a drop in blood pressure on standing, from dehydration, medicines or autonomic problems
Cardiac syncope, caused by arrhythmias (too fast or too slow) or structural heart disease such as aortic stenosis or cardiomyopathy
Cardiac syncope carries the highest risk, which is why a first faint, particularly with warning signs or exertion, deserves a proper heart assessment.
The circumstances around a faint give the most valuable clues about its cause.
Typical of a common (vasovagal) faint
Triggered by standing for a long time, heat, a crowded place, pain, the sight of blood or emotional stress
Warning symptoms: light-headedness, nausea, sweating, pallor, blurred or tunnel vision, ringing in the ears
Recovery within a minute or so once lying flat, sometimes with tiredness afterwards
Typical of orthostatic faints
Dizziness or fainting on standing up from lying or sitting
Worse after meals, in heat, after alcohol or with dehydration, or after starting blood pressure medicines
Features that suggest a heart cause
Fainting during exercise, or when lying down
Sudden faint with no warning, or preceded by palpitations or chest pain
Injury from falling, or a family history of sudden death under 40
Known heart disease, an abnormal ECG or a heart murmur
Fainting has many causes, grouped by mechanism.
Reflex causes
Vasovagal (common faint), triggered by standing, heat, emotion, pain, blood or needles
Situational faints with coughing, swallowing, passing urine or after exercise
Carotid sinus hypersensitivity, mainly in older people
Blood pressure and volume causes
Dehydration, blood loss and heat
Medicines (blood pressure tablets, diuretics, antidepressants, nitrates) and alcohol
Autonomic nervous system conditions, Parkinson’s disease and diabetes
Heart causes
Arrhythmias: slow rhythms (sick sinus syndrome, heart block) or fast ones (ventricular tachycardia, supraventricular tachycardia, long QT, Brugada syndrome)
Structural disease: aortic stenosis, hypertrophic cardiomyopathy, heart failure, pulmonary embolism and pulmonary hypertension
Conditions that mimic fainting
Seizures, low blood sugar, intoxication and concussion can cause loss of consciousness, and are assessed differently.
A careful history is the most important part of the assessment, supported by selected tests.
1. History, examination and standing blood pressure
Details from you and any witness are crucial: what happened before, during and after, how long it lasted, and your medicines and family history. Lying and standing blood pressure checks look for orthostatic hypotension.
2. ECG
A 12-lead ECG looks for conduction disease, pre-excitation, long QT, Brugada pattern, signs of cardiomyopathy and previous heart attack.
3. Echocardiogram
An echocardiogram checks for structural heart disease, such as aortic stenosis, cardiomyopathy and a weak heart.
4. Rhythm monitoring
Cardiac monitoring by Holter, patch, event recorder or implantable loop recorder looks for rhythm disturbances when faints are infrequent, and is guided by how often they occur.
5. Further tests
Tilt-table testing when reflex syncope is suspected but unproven
Exercise ECG or stress echo when fainting occurs with exertion
Carotid sinus massage in older people, blood tests, and cardiac MRI when cardiomyopathy is suspected
Treatment depends on the cause, and most people need education and simple measures.
Reflex (vasovagal) syncope
Education and reassurance, and recognising and avoiding triggers
When you feel a faint coming on, lie down or sit, and use physical counter-pressure manoeuvres such as leg crossing with muscle tensing, or hand-gripping, which can abort an episode
Adequate fluid (2 to 3 litres daily) and salt intake, unless you have high blood pressure or heart failure
Medicines such as midodrine or fludrocortisone for selected people with frequent faints, and review of blood pressure medicines
Pacing in selected older people with documented pauses in the heartbeat
Orthostatic hypotension
Rise slowly, drink enough fluid, avoid alcohol and large meals, use compression stockings, and review or change medicines that lower blood pressure. Medicines such as midodrine can help in selected people.
Cardiac causes
Pacemaker for syncope due to sick sinus syndrome or high-grade heart block
Catheter ablation for SVT and some other arrhythmias
Implantable defibrillator (ICD) and medicines for dangerous ventricular rhythms
Valve replacement for severe aortic stenosis, and treatment of cardiomyopathy or heart failure
Learn your warning signs and lie down immediately, ideally with your legs raised, to avoid injury.
Avoid triggers: long periods standing still, hot environments, dehydration and alcohol.
Drink plenty of fluids, and keep up regular meals.
Rise slowly from lying or sitting.
Review medicines with your doctor, particularly blood pressure tablets.
Driving: DVLA rules depend on the cause and whether there was a warning. Do not drive until you have been advised, and tell your insurer.
Work and safety: avoid heights, swimming alone and hazardous machinery until the cause is understood.
Support is available from STARS, the British Heart Foundation and the NHS.
Most people who faint have reflex syncope, which has an excellent outlook, though it can recur and affect quality of life.
Orthostatic hypotension is usually manageable and often improves with simple measures.
Cardiac syncope carries a higher risk, but once the cause is identified, effective treatments such as pacemakers, ablation, ICDs or valve surgery can substantially reduce it.
Outlook depends on the underlying cause and any heart disease, which is why a proper assessment matters.
The commonest risk in reflex faints is injury from falling, so safety measures matter.
Everyone who has fainted without an obvious benign explanation should have it assessed at least once.
Arrange an assessment if you have:
A first unexplained faint, or recurrent faints
Dizziness or near-fainting that is frequent or interferes with life
Faints with injury, or at risk of injury (driving, working at heights)
Known heart disease, a murmur or an abnormal ECG
A family history of sudden death, fainting or an inherited heart condition
Fainting after starting or changing a medicine
Usually benign if:
It occurred while standing for a long time, in heat, with pain, or at the sight of blood, with typical warning symptoms and a quick recovery, and you have no heart disease, abnormal ECG or family history.
These features suggest a higher risk of a cardiac cause, and call for an urgent assessment.
Red flags
Fainting during exercise or while lying down
Fainting with no warning, or after palpitations or chest pain
Breathlessness or chest pain associated with the faint
Known heart disease, heart failure, a murmur or an abnormal ECG
Family history of sudden death under 40, cardiomyopathy or long QT syndrome
Several faints in a short time, or a significant injury
What to do
Arrange an urgent consultation, an ECG and an echocardiogram, ideally within days. Keep a note of what happened and ask a witness to describe it.
Fainting with the following needs emergency help.
Call 999 immediately if someone has fainted and:
Has chest pain, severe breathlessness or palpitations
Does not wake up promptly, or has a seizure, confusion or weakness on one side
Fainted during exercise, or has injured their head or chest
Is pregnant, has a known heart condition, or has a very slow or irregular pulse
If someone has collapsed
If a person is unresponsive and not breathing normally, call 999, start CPR and use a defibrillator if available.
Fainting (syncope) is a temporary loss of consciousness caused by reduced blood flow to the brain.
Most faints are reflex (vasovagal) and harmless.
Faints with exercise, no warning, palpitations or chest pain suggest a heart cause.
A careful history, ECG, standing blood pressure and echocardiogram are the key tests.
Rhythm monitoring or a tilt test may be needed.
Reflex faints are managed by avoiding triggers, fluids and counter-pressure manoeuvres.
Cardiac causes are treated with pacemakers, ablation, ICDs or valve surgery.
Lie down when you feel faint, to avoid injury.
Driving restrictions may apply until the cause is clear.
Guidelines and sources
This page follows current UK and European guidance:
NICE CG109: Transient loss of consciousness (blackouts) in over 16s.
Brignole M et al. 2018 ESC Guidelines for the diagnosis and management of syncope. European Heart Journal 2018;39:1883-1948.
DVLA: Cardiovascular disorders: assessing fitness to drive (GOV.UK).
These are the questions patients most often ask about fainting.
What causes fainting?
Most commonly a reflex drop in blood pressure and heart rate (vasovagal), or a drop in blood pressure on standing. Less commonly, a heart rhythm problem or heart disease.
Is fainting dangerous?
Usually not, but a faint caused by the heart can be, which is why a first faint, or one with warning signs, should be assessed.
What should I do if someone faints?
Lay them flat and raise their legs. Check breathing, and recovery should be within a minute or two. Call 999 if they do not recover quickly, are not breathing normally, have chest pain or have injured themselves.
What is the difference between fainting and a seizure?
A faint is usually brief with a quick recovery and limp collapse, while a seizure often involves prolonged jerking and confusion afterwards. The two can look similar, and a witness description helps.
When should I see a cardiologist after fainting?
If it happened during exercise or without warning, with palpitations or chest pain, if you have heart disease or an abnormal ECG, a family history of sudden death, or you have fainted more than once.
What tests are done for fainting?
Standing blood pressure, an ECG, an echocardiogram, blood tests, and often rhythm monitoring. A tilt-table test or exercise test is used in selected people.
How can I stop myself fainting?
Recognise the warning signs and lie down, drink plenty of fluids, avoid triggers, and use leg crossing or hand-gripping to raise blood pressure. Medicines or a pacemaker are used for selected people.
Can I drive after fainting?
It depends on the cause and DVLA rules. A simple faint with a clear trigger may have no restriction, whereas unexplained faints usually require you to stop driving. Take advice and inform your insurer.
Can I have a private assessment for fainting or blackouts?
Yes. A telephone, video or face-to-face consultation in Peterborough or Corby can assess your faints, with ECG reporting, echocardiography and cardiac monitoring arranged as needed.
- What type of faint did I have, and what caused it?
- Could it be due to my heart?
- Which tests do I need?
- What can I do to prevent another faint?
- Do I need a monitor, a pacemaker or other treatment?
- Is it safe for me to drive, exercise and work?
- Should my family be checked?
- Could any of my medicines, or low blood pressure on standing, be contributing?
- What should I do if I feel a faint coming on?
- How often will I be reviewed, and when should I come back sooner?
What happens during a faint
Most faints follow the same sequence. Blood pressure and heart rate fall, the brain briefly receives too little blood, the person collapses, and lying flat restores blood flow.
Reflex, blood pressure or heart cause?
The circumstances of a faint are the best clue to its cause. These are clues only, and a doctor confirms the cause.
How a faint is assessed
A careful history and a few targeted tests are usually enough to find or exclude a heart cause.
What to do if you feel faint, or someone faints
Knowing what to do can prevent injury and can sometimes stop a faint from developing.
If you have fainted or had unexplained blackouts, you may benefit from a telephone consultation or video consultation to discuss your symptoms in detail, or a face-to-face consultation in Peterborough or Corby for a more comprehensive assessment.
Investigations such as ECG, cardiac monitoring and echocardiography may be recommended.
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Medically reviewed by Dr Salam Salloum, Consultant Cardiologist. Last updated: . This page is for general information and does not replace personal medical advice.